This invention relates to an electronic control system for an internal combustion engine, and more particularly to an electronic engine control system which improves quick responsiveness of engine torque to acceleration under various operating conditions of the engine.
First, various problems encountered hitherto at the time of acceleration of a vehicle equipped with an internal combustion engine will be discussed.
At the time of acceleration of such a vehicle, a delayed response to acceleration which is called a hesitation, a sudden output drop during acceleration which is called a stumble or sag, low frequency vibration in the longitudinal direction of the vehicle which is called an accelerating surge, etc. tend to occur and give the vehicle driver a feeling of discomfort.
Leanness of the air-fuel ratio in the air-fuel mixture supplied to the engine at the time immediately after acceleration is said to be a principal cause giving rise to these phenomena, and employment of a variable venturi type carburetor based on a method of independent fuel injection (sequential fuel injection) is reported in, for example, a magazine entitled "Automobile Techniques" Vol. 39, No. 9, pp. 1001-1005, 1985.
Also, a technique of electrically controlling the opening of a throttle valve according to the amount of depression of an accelerator pedal is reported in, for example, "Automotive Engineering", June 1982, p. 98 and "IEEE, IECON" 1985, pp. 101-105. However, improvements in the operation performance of an internal combustion engine during acceleration have not been considered much in these publications.
Thus, although the driver and other occupants of a vehicle feel that the vehicle is being accelerated only when the vehicle is driven in its advancing direction under acceleration, such acceleration has not been considered at all hitherto. (Acceleration in the advancing direction will be referred to hereinafter merely as acceleration.) That is, in spite of the fact that acceleration of the vehicle is an important factor which dominates the feeling of the vehicle driver and occupants as to whether they feel comfortable or not, the prior art proposals have not been satisfactory in that the will of the driver who intends to accelerate the vehicle is not immediately perceived and reflected, and the vehicle cannot be immediately accelerated. Therefore, it has been strongly demanded to achieve acceleration of a vehicle in response to the will of the vehicle driver, that is, actuation of an accelerator pedal thereby improving the acceleration performance, and to minimize occurrence of the phenomena including the accelerating surge thereby freeing the driver and occupants from the feeling of discomfort.
Next, ignition timing control by a prior art engine control system will be discussed. In the prior art system controlling an engine, the ignition timing is controlled according to various factors including the load of the engine, for example, the rotational speed of the engine and the quantity of intake air per suction stroke of the cylinder. The ignition timing is controlled under the condition that the opening of a throttle valve is in its steady state or constant. Therefore, in a transient state in which the throttle valve opening is continuously changing as when the vehicle is being accelerated or decelerated, proper ignition timing control cannot be attained, and the engine torque cannot quickly respond to the acceleration or deceleration. Thus, the prior art engine control system has been defective in that the vehicle cannot be quickly accelerated and decelerated.
Idling rotation speed control in the prior art engine control system will then be discussed. When, during idling of the engine, the rotational speed of the engine changes due to a load variation, an idling speed control valve (ISCV) or the throttle valve is actuated so as to restore the engine speed to its desired idling rotational speed. However, the prior art engine control system has been defective in that the engine torque cannot quickly respond to the load variation, and the engine speed is restored to the desired idling rotational speed with a considerable delay time.